Color television system



Sept. 29 1942. E. CROSBY L COLOR TELEVISION SYSTEM 2 Sheets-Sheet l Filed Des. 10, 1940 YBY Sept. 29, 1942. E. CROSBY COLOR TELEVISION SYSTEM 2 SheetS-Sheer. 2

Filed Des. 10, 1940 INVENTOR EVERETT c os B W//////////////////////////////// Vfl/ IIIIIIIIIIIIIIIIIIII Patented Sept. 29, 1942 UNITED STATES PATENT OFF!CE COLOR TELEVISION SYSTEM Everett Crosby, New York, N. Y.

Application December 10, 1940, Seria.l N0. 369,393

9 Claims.

My present invention relates to television. A general object of my present invention is to provide improved apparatus and methods for the transmission by means of electricity, magnetism or electromagnetic waves, of pictures, photographs or images cf stationary or moving objects x the like in natural colors.

Still other general objects of my invention are to provide an improved system of television in which ultimate reproduction is in the natural colors of the images transmitted, to provide an improvea transmitting system for the transmission of television in color and to provide an improved receiving system and apparatus for receiving television in color.

Other objects, es weil as advantages and l'eatures of my present invention, will be apparent as the more detailed description thereof proceeds. The latter will be given with the aid of the accompanying drawings in which:

Figure 1 is a schematic diagram of one form of my improved color television transmitting system;

Figure 2 is a schematic plan view of one type of a muiti-color elementary screen used in counection with the transmitter and receiver of my system; and

Figure 3 is a schematic diagram of one embodiment of my improved television co1or receiving system.

In order 130 understand my present invention in greater detail, the steps and apparatus for picking up, transmitting and reproducing a color television picture Will now be given.

Rcferring to the transmitting ystem 0f Figure l, an object t0 be transmitted in co1or, diagrammatically illustrated ab O, is illuminated by the incandescent lighting system ILS. Light refiecaed from the object 0 is collected by a suitab1e 1ens system L and fccussed on thelefl; side cf plate P of the television camera taube T of the two sided iconoscope type. The camera tube T, however, differs from the normal type of two sided iconoscope by the provision of a. tri-cclor screen system TCS, the nature and function of which will be explained more fully later.

The platze P is made in such a way that fihoto emission takes place Irom one side, namely, that nearest the 1ens system and the electron beam B scans the other. For a more detailed description of the conventional portion of the two sided iconscope taube T, its conventional or usual type of collectin ring CR, p1ate P, electron gun EG and anode AN, reference is made to a book entitled Television by V. K. Zworykin and G. A.

Morton, published by John Wiley and Sons, Inc. New York (1940) page 302, et seq. In rny invention, the collector ring CR is so mounted in ge ometric or space relationship to the color screen TCS and the photo sensitive surface of the plate P thatthe emitted photo electrons can be readily withdrawn approximately radialiy from the Space between TCS and P, thus minimising false picture shading efiects.

The scanning may be accomplished by deflecting the electron beam B, projected fr0m the electron gun EG, electromagnetically by means of the horizontal coi1 HC and vertical coi1 VC external to the tube T. If desired, of course, the beam B may be deflected electrostatically. The coi1s HC and VC are excited with currents derived from the horizontal defiecting circuits and apparatus HD, vcrtical deflecting circuits and ap-paratus VD and synchronizing generator SG.

The currents applied to coils HC and VC are of frequencies and wave shapeg such as to cause the point of impact of the electmn beaxn B upon platze P to move across the two-sided' mosaic 01' plate P in approximately a horizontal line at uniform speed, then fly back (blanked out 01 extinguished during the return periods) and scan another line and so on unti1 the entire mosaic or plate has be'en scanned by, for example 441 lines in the desired sequcnce. The complete scanning is repeated at a rate of preferably thirty times per second, 0r 13230 lines per second.

The resulting video voltage pulses Set up across the coupling resistor CPR. are fed, together with pulses from the synchronizing generator SG, into the amplifying sysbem A. The latter is connected to the radio transmitter RT and serves modulate wibh the complete picture signal, including the synchronizing signals, the radio waves transmitted over the transmitting antenna TA.

In order to transmit the Video program in color, in accordance with my present invention, a tricolor disc-like s:reen TCS is mounted within tube T in any suitable way, as, for exarnple, by means of an annular glass bead GB. As shown in plan view Figure 2, the t1i-color screen TCS may be mcunted upon er otherwise supported by a transparent carrier (for example, of g1ass) TRC in turn carried by the glass bead GB (er other form of support) of Figure 1. The color transmitting pa.rt of the system of Figure 2 consiscs of parallel, equally high or thick strips of material r, g, b which transmit on1y the primary colors red, green and blue. The strips or color elements r, g, b are arranged and repeatcd systematically.

rallel to and centered on the color filter lines.

The linear scanning direction SD is preferably perpendicular to the color filter lines, unless multiple interlace systems of scanning are used, as described below, in which case SD should be pa- In one embodiment of my invention, single series of the strips r, g, b; namely, a Single red, a single green and a single blue strip, are of such size that together they are equal 1:0 the height of the normal spot size or height employed in the beam for the transmission of ordinary black andwhite elevision and the scanning spot size is correspondingly reduced to one-third of that for correspondin'g black and white television. This permits transmitting a color picture wherein the fineness of detail for each color is equal to that of the corresponding blank and whlte pictur, thus permitting viewing of the received color picture at about the same distance as for blank and white pictures. Alternatively, the strips 1', g, b may be each o1 -the height of the normal scanning spot for black and white television and the scanning spot size may be the same as for black and white television. In this case the color structure of the received picture will be more conspicuous and therefore it must be viewed for satisfaction at a greater distance to avoid intrusion of the color-elementary structure. The strlps r, g, b may be colored glass filaments or plates laid parallel and adjacent to each other o1 they may be different colored gelatines covered by and within a transparent non-gas-porous hermetically sealed coating or housing which may in turn be placed between two glass plates with hermetically sealed edges. Obviously, as illustrated, the color filter strips shown in section in Figures 1 and 3 and in plan in Figure 2, have been greatly exaggerated in size so as to facilitate understanding and description thereof. It is here emphasized that, while a linear structure of the color filter elements has been shown, any other color filter structure may -be substituted withln the scope of my invention provided the elements are not larger than will give sufiiciently fine color detail for viewing of the received picture. and provided they are capable of systematic and identical arrangement on the transrnitting and receiving color filters respectively, and are capable of identical synchronized scanning regimes at the transmitter and receiver.

II: is 120 be noted that the tri-color elementary screenTCS is at a finite separation from the photo sensitive surface of the platze P and is mounted within the evacuated chamber of tube T. However screen TCS should be as close to the photo sensitive surface as is feasible consldering the electrical function of collector CR.

It will be observed that by the system outlined above, the illumination of the photo sensitive surface of plate P will vary not only with intensity, but also with color. Thus, as the beam scans a line immediately in the rear of a red element of the tri-color screen TCS, the voltage pulses arising across coupling resistor CPR indicate varying intensities or complete absence of red an the object O. As the next adjacent color line 18 scanned, the pulses across resistor CPR indicate the intensity of green reflected from the object O, the next line blue and then the process is repeated until the whole platze P is scanned when the process at the transmitter is repeated.

At the receiver, as shown in Figure 3, there is placed, resting upon or at a finite separation from, and immediately in front of the usual white fluorescent screen WFS, a tri-color fllter or screen RTCS similar and homologous 120 that employed at the transmitter. The color screen RTCS at the receiver may be placed outside of the cathode ray tube ORT and adjacent the fluorescent screen WFS or both may be mounted within the evacuated portior'1 of the cathode ray tube.

The remainder of the receiving system is generally conventional and consists of a receiving 'antenna RA and a superheterodyne type of radio receiver RR. The picture components are ampllfied in th latter and then separater], as shown, and utilized for operating the vertical and horizontal deflecting apparatus as well as the picture and brightness control system PBC.

' The tri-color elementary screen at the receiver is homolog0us and similar to the tri-color filber TCS, as before stated. The receiving system is provided with precise but conventional means for precise adjustment cf picture size and position upon the fluorescent screen in relation to the tricolor elements of the tri-color elementary screen. The receiving system of Figure 2 also is provided with suitable means for adjusting the degree of linearity of the deflection versus time curves for the horizontal and vertical scanning at the receiver to give -correspondence of such degree o! linearity at the receiver with that at the transmitter. Linearity controls are well -known and need not be further here described. (See, for example, the peaking or linearity control shown in Figure 17.35, page 553, Z worykin and Morton, cited above).

vMoreover, in one preferred operation of my color television system, three-to-one interlacing is provided for, at trans mitter and receiver, it being noted that each interlace scanning corre sponds to a single primary color component; in the transmitter and also corresponds to the identical primary color component scanning at the receiver.

In this embodiment, the color filters are horizontal lines or narrow strips, parallel to the scanning direction, and cf a vertical width effectively equal to that of the scanning spot which is centered on the lines in its passage or traversal across the picture. Interlaced scanning per se is well known in the art and neecl not be further described.

Any number of diflerent colors, such as two four, flve, etc., may, of course, be used recurrently in the color filter systems, as found desirable although I prefer to employ the three specified. Also in operating, as explained, I prefer to make the color elements small as compared to the regulation size of picture element. Thus, ordinary 44l-line scanning would have a spot size three times that employed herein. However, it is to be understood that the system described herein may use the same size spot; or 441- line scanning, without requiring increased channel space and which would also permit use of my color System in conjunction with proposed television systems and apparatus with a minimum change in apparatus and operation.

can be satisfied by proper electzron gun design and focusing of the scanning spots atz tzhe transmitter and receiver. Secondly, at all tzimes, tzhe scanning spot ppsition in relation to tzhe red, green and.blue filter lines or elementzs mustz be identzical atz the t'ransmitzter and receiver. This is accomplished by exact adjustzmentz cf picture widtzh and heightz and exact adjustmentz of the scanned area relative to color elements, and also by fine adjustmentz f the defiectzion controls; namely, the defiection voltzages for electzrostatic deflectzion er deflectzion' currents for magnetzic deflectzion, which has been illustrated in the drawings. 'I'his also entzails the utilization cf coustant directz current voltages for electzrostatzically controlled tzubes or constzantz directz current sources for the magnetically contzrolled tubes enabling the provision qf fine adjustments for tzhe cent:ering controls atz tzransmitter and receiver Another condition tzo be satzisfled, as statzed above, is identzical linearltzy (er curvature) of tzhe deflectzion waves at transmitzter and receiver during the scanning interval. This control is well known tzotzhe artz and generally is accomplished by adjusting tzhe circuitz constantzs 01 the saw-tootzh oscillators employed and the associated amplifiers in the deflection systems.

Reference has already been made to color interlacing. In this event, the scanning spot should be no wider than a single color line and, furtzhermore, tzhe scanning spot: should move strictzly along color lines. Assuming itz is desired to have a three'-to-one interlace, the scanning sequence would be arranged as follows:

Red (scanning N0. 1) lines l, 4, 1, lt), Green (scanning N0. 2) lines 2, 5, 8, II. Blue (scanning N0. 3) lines3, I5, 9, I2, Red (scanning N0. 4) lines I, 4, l, III, etc.

- to tzhis positioning thereof. Thus, if inc0n0sc0pe T is of the so-called "image inconoscope type (see Zworykin and Mortzon, pages 313 et seq.), tzhe color screen TCS may be placed betaween the semi-tzransparentz photzo catzhode of tzhe iconoscope on which catzhode the image is Hamed and the lens forming the image, and preferably in air as close as possible to the glass surface carrying the photo catzh0de. Alternatively, instead of being a tz or near tzhe outer boundary 01 this surface and in air, the color screen may be on or near tzhe inner boundary 01 this surface and in vacuum, the photzo cathode belng tzhen deposltzed or positioned on 01' near the sald color screen 5 Numerous similar modiflcatlons in tzhe post mitting the voltzage pulses set up in said plate.

tzion of the color screen relative to tzhe transmitzter or reproducing or pictzure tubes at the receiver will readlly be apparentz and fall witzhin tzhe scope of my inventzion.

Having thus described my -invention, what I claim is:

l. In a color television system, tzhe combinatzion of a lens system and a cathode ray scanning oscillograph comprising an evacuated envelope, a photosensitive platze mounted within the envelope substantially in the focal plane of the lens systzen1, and a. multzlcolor elementary light filter mountzed witzhinthe envelope and spaced minute- 1y from tzhe plate on the side of the lens system, the fi1ter elements being substantially coplanar.

2. In a color television system, tzhe combinatlon of a lens systzem and a cathode ray scanmng oscillograph comprising an evacuated envelope, a photosensitzive plate mounted witzhin tzhe envelope substantially in tzhe ideal plane cf the lens system, and a multzicolor elementary lightz filter mounted witzhin tzhe envelope and spaced minutely from tzhe platze on the side of the lens system, tzhe filter being platze-like with a single element across any thickness thereof.

3. In a color television System, the combination of a lens systzem and a cathode ray scanning oscillograph comprising an evacuatzed envelope, a photzosensitzive platze mountzed witzhin the envelope substantially in tzhe focal plane of the lens system, and a multicolor elementary lightz filtzer mounted within the envelope spaced. minutely Irom the platze an the side of the lens system, and disposed substantzially in the focal plane of tzhe lens system.

4. The combination setz forth in claim 1 and further comprising an anodic ring electzrode between the plate and fi1tzer.

5. The combtnatlon Set fortzh in claim 1 and furtzher comprising an anodic ring electrode Joetzween the plate and filter, and means for trans- 6. The combinatzion setz fortzh in claim 1, tzhe filtzer elements being dimensloned to permitz a scanning spot tzo fall within each element.

7. The combination set fortzh in claim 1, in which tzhe light filter comprises groups 01 color stripsthe strips of each group being of difierentz colors and having a small dlmension substantlally equal to a scanning spotz.

8. The combinatzion setz fortzh in claim 1, in which the lightz filtzer comprises groups of color strips, the strips of each group being of dttferentz colors and having a small dimension substantzlally equal to a scanning Spot and means for scanning said plate transversely of said strips.

9. In a color television system, a catzhode ray scanning oscillograph, comprising an evacuated envelope, a photosensitive plate mountzed wltzhin tzhe envelope, and. a. multicolored elementary lightz filtzer associated witzh tzhe platze and mlnutely spaced trom the far face 01 tzhe platze relative to tzhe catzhode ray gun, the ftlter comprlstng groups o! color strips having one dimension coextzensive with the platze and. having a small dimension substantially equal tzo a. scanning sp0t.

EVEREI'I CROSBY. 

